THis was a great treadmill until the frame cracked and they would not honor the lifetime warranty. the frame is composed of 2 parts joined by bolts so that the belt can rise on an incline. The one half where the belt is is called a frame and the other half is the lift frame. Both are construced of the same material. The lift frame on our treadmill cracked and they want 150 for it. I have read several other complaints of these lift frames cracking. Shame on NordicTrack. This is my second unit and I would rather buy another brand than spend the 150 on the "lift frame".